URL formula to open outlook meeting

I believe you are asking about what is called a protocol handler. The Outlook protocol handler  supports links to various components of Outlook and have the form outlook: which might be used like this from a web page:

<a href="outlook:inbox">Outlook:inbox</a>

But Microsoft claims you can only use these links between components of Outlook (since 2013). Some people say you can still use these links if you modify the registry (I believe this is still true). You can read about the issue here:

Outlook 2007 and "Outlook://" protocol
https://social.technet.microsoft.com/Forums/office/en-US/ac69a8cc-c411-4f82-8fe8-8ccd4554964d/outloo...

Playing with the registry is very tricky business and it depends highly on your version of Windows and Office. I would not suggest you attempt this unless you know what you are doing.